Conventional access to the features and services provided by GSM and UMTS networks involves signalling between the mobile terminal and a standard base station (macro base station) that has a dedicated connection to an MSC and provides coverage in the cell occupied by the mobile terminal using cellular telecommunication (e.g. GSM or UMTS) transport protocols. There have recently been proposals to allow access to the features and services provided by GSM and UMTS networks by providing additional special base stations (femto base stations), referred to as access points (APs), for example at a subscriber's home, in order to increase network capacity. These access points communicate with the core network via IP based communications, such as a broadband IP network, and are typically routed via the Internet.
Many different names have been given to APs, such as home access points (HAPs), micro-base stations, pico-base stations, pico-cells and femto-cells, but all names refer to the same apparatus. APs provide short range, localized coverage, and are typically purchased by a subscriber to be installed in their house or business premises.
It has also been proposed to use APs in the Long Term Evolution (LTE) telecommunications network currently being developed, but not yet implemented. LTE is likely to be the next network implementation after 3G.
An advantage of introducing APs in existing telecommunications networks is that, where sufficient numbers of APs are implemented, the power level of the macro coverage could be reduced, due to a lower demand for the macro-base stations. Power reductions of course result in financial savings.
A further advantage of using an access point connected to the core network via an IP network is that existing broadband Digital Subscriber Line (DSL) connections can be used to link mobile terminals with the network core without using the capacity of the radio access network or transmission network of a mobile telecommunications network. In other words, the AP is integrated into a DSL modem/router and uses DSL to backhaul the traffic to the communication network.
A still further advantage is that APs are able to provide mobile network access to areas where there is no radio access network coverage. Thus, they are expected to be particularly beneficial when installed in buildings with poor radio network coverage from the macro network but which have DSL connections. Additionally, an AP could provide UMTS coverage where there is no 3G coverage at all, perhaps only GSM coverage.
However, since these access points are not conventional base stations, additional challenges arise. In particular, since the access points are typically deployed in environments not directly under the control of the network provider, it is desirable that the security of these access points can be guaranteed for each subscriber making use of them.
Currently, telecommunication network providers sometimes offer subscribers different call tariffs based on their location. For instance, one such service provides subscribers with cheaper tariffs when they use their mobile terminal in their home.
With reference to FIG. 3, in one known implementation of such a system, upon a subscriber subscribing to a reduced tariff service, the core network 140 identifies which base stations, and hence which cells, provide coverage to the subscriber's home. These base stations are referred to as the subscriber's home base stations. Each base station has a unique cell ID and the unique cell IDs of these home base stations are logged against the subscriber's profile. In the example of FIG. 3 the base stations with cell IDs 1245 and 1234 provide coverage over the subscriber's home and are therefore recorded alongside the subscriber's profile in the network database 160. Base station with cell ID 1256 is not recorded as a home base station as it does not provide coverage over the subscriber's home.
Therefore, when the subscriber is communicating on the mobile network and is located within his home, the subscriber's communication traffic will be routed from either of the home base stations having cell ID 1245 or 1234, through the Controller (e.g. a Radio Network Controller (RNC) in 3G) 130 and onward to the core network 140, which includes MSC 135.
During the call set up procedure, the core network will receive the MSISDN of the subscriber and the cell ID of the base station with which the subscriber is communicating. In order to confirm at which rate to change the subscriber, the core network 140 checks whether the subscriber is using one of the home base stations which cover his house 10. This check is made by consulting the Location Based Charging (LBC) Module 150 and database 160 and by comparing the MSISDN and cell ID identified in the call with those stored in the database. If the cell ID for the MSISDN is the ID of one of the subscriber's logged home base stations, the subscriber is recognised as calling from within his home and is charged at a reduced rate, otherwise he is charged at his standard rate. In the example of FIG. 3, the reduced rate will be applied when the subscriber's call is routed through base stations 1245 and 1234 but not when the call is routed through base station 1256.
With this in mind, APs provide another opportunity for network providers to offer reduced rates to subscribers. For instance, subscribers may benefit from a different call tariff when using their mobile terminal through an AP acting as a base station.
Further additional challenges arise in implementing these access points as conventional base stations, in view of their potential mobility. Ideally APs are introduced into a telecommunications network and remain fixed at that site. However, there is the possibility that subscribers may decide to relocate their access point for use at a different site. This would be problematic where the subscriber obtains a reduced tariff for using their AP as a base station from their home, as potentially they would be able to also receive the reduced tariff at other locations by relocating the AP. There is therefore the need for determining the location of an AP in order to determine whether or not a reduced tariff is to be used.
A further problem in regard to the mobility of APs is that mobile telecommunication providers are allocated spectrum in specific regions, so it is vital that they are able to identify the location of all their base stations, which includes APs, since APs are functionally equivalent to macro base stations. In fact, proposed regulatory regulations are likely to require telecommunications providers to know the location of all access points in their network. There is therefore also a need to determine the location of an AP before allowing a communication to proceed or before an AP is activated.